Gap between crankshaft and bottom bracket bearings. Does this look right?
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Gap between crankshaft and bottom bracket bearings. Does this look right?
Three year old Cannondale Synapse 5, FSA triple chainset with a MegaExo bottom bracket. The LBS said the changed the bottom bracket bearings about two months ago. A clicking noise returned about a month later. Pulled the chainset and found A) a 1.5 mm gap between the inner bearing race and the shaft and B) the right bearing is making a growling sound in certain spots when turned by hand. Honestly, I'm not so sure they put in the right bearings. Does this look normal?
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No, for the bearing (or ANY bearing) to work properly, the axle must be supported with a tight fit. Otherwise it will flex, possibly leading to fatigue and failure (snapping under load).
You need to replace 2 items
1- the bearing (and possibly it's mate on the other side
2- the mechanic who considered this OK.
BTW- it's possible that the bearing is correct, but a shim of some kind was omitted (I don't stay up with every BB or crankset), but the effect is the same. Also check the other side, since riding this way would have stressed the other bearing causing excess load and wear.
You need to replace 2 items
1- the bearing (and possibly it's mate on the other side
2- the mechanic who considered this OK.
BTW- it's possible that the bearing is correct, but a shim of some kind was omitted (I don't stay up with every BB or crankset), but the effect is the same. Also check the other side, since riding this way would have stressed the other bearing causing excess load and wear.
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“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
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No, for the bearing (or ANY bearing) to work properly, the axle must be supported with a tight fit. Otherwise it will flex, possibly leading to fatigue and failure (snapping under load).
You need to replace 2 items
1- the bearing (and possibly it's mate on the other side
2- the mechanic who considered this OK.
BTW- it's possible that the bearing is correct, but a shim of some kind was omitted (I don't stay up with every BB or crankset), but the effect is the same. Also check the other side, since riding this way would have stressed the other bearing causing excess load and wear.
You need to replace 2 items
1- the bearing (and possibly it's mate on the other side
2- the mechanic who considered this OK.
BTW- it's possible that the bearing is correct, but a shim of some kind was omitted (I don't stay up with every BB or crankset), but the effect is the same. Also check the other side, since riding this way would have stressed the other bearing causing excess load and wear.
The bearing on the other side is the one that is growling and has a rough spot when you turn it by hand.
I'm going to A) Order a new MegaExo bottom bracket and B) Dump the mechanic. It's not the first time he has unwittingly screwed up but I've learned enough now to maintain it on my own.
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My guess is your LBS screwed up on the left side as MegaExo has a different bearing on the left than the right; the MegaExo has a tapered spindle that is 24mm on the drive side and 22mm on the left. Due to the fact that you have been riding this way it no doubt has trashed the right side bearing.
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My guess is your LBS screwed up on the left side as MegaExo has a different bearing on the left than the right; the MegaExo has a tapered spindle that is 24mm on the drive side and 22mm on the left. Due to the fact that you have been riding this way it no doubt has trashed the right side bearing.
BTW- the asymmetrical bearings explain how the mistake happened, but not why it happened. The why relates to poor mechanic training. The mechanic knew how to assemble a BB following a sequence of steps, and probably using a torque wrench. When all was OK he could turn out reasonable work, but because he didn't understand how BBs work he didn't spot what should have been an obvious problem.
This is an example of what is becoming altogether too common, and what I call GPS training. Mechanics can do the work, but don't really understand how things work. I call it GPS knowledge by analogy to how people navigate today. Imagine two people from Chicago to Portland. One knows US geography and the other doesn't. They both plug Portland into the GPS and start out on I-90 as instructed. The difference is that one driver seeing the "Welcome to Indiana" will quickly realize that Portland Oregon is the other way, but the other may not realize the error until he's in Maine.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
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Perhaps I can understand this for angular contact cone bearings, but these are radial cartridge bearings that require no axial preload. The crank spindle is held in alignment by it's close fit to the inside of the inner races and won't wobble or deflect, unless it bends. I would think the spindle would need a lot more overhand than that to bend under normal pedaling loads.
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Perhaps I can understand this for angular contact cone bearings, but these are radial cartridge bearings that require no axial preload. The crank spindle is held in alignment by it's close fit to the inside of the inner races and won't wobble or deflect, unless it bends. I would think the spindle would need a lot more overhand than that to bend under normal pedaling loads.
Since the OP says the right bearing is now rough, we can take that at face value regardless of the cause, though I suspect that side wear is the issue. I have mixed feelings about the spindle. If when he removes the spindle, the OP finds scoring or wear inboard of the right bearing, I think he'd be within his rights to ask the dealer to replace the crank. At the very least, he should contact the maker for an opinion on that matter. If the spindle looks OK then it probably is since either way the greatest stress (normally) is outboard of the bearing, so it may not make a difference.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
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If when he removes the spindle, the OP finds scoring or wear inboard of the right bearing, I think he'd be within his rights to ask the dealer to replace the crank. At the very least, he should contact the maker for an opinion on that matter. If the spindle looks OK then it probably is since either way the greatest stress (normally) is outboard of the bearing, so it may not make a difference.